The benefits of two-leg versus three leg power control, in three phase heating applications
The global glass industry needs to continue reducing its carbon footprint, either driven by customer initiatives or forced through environmental legislation. Improvements to traditional fossil fuel-fired melting systems reached peak capability around the turn of the century, so complying with stricter CO2, NOx and SOx emission legislation remains an ongoing challenge.
Even with the use of complex and expensive add-on systems, it is becoming difficult to achieve targets. Electrical heating (an electron approach), or the use of alternative fuels such as hydrogen (an atom approach), look like the most sensible options. This could be through a combination of adding electrical furnace boosting to a hybrid melting system or fully switching to all-electrical methods. As explained in many publications, this will not be an easy progression. Nevertheless, in many regions it is already feasible.
Towards zero emission processes
Over the past couple of years, there has been a lot of discussion about the transition of glass manufacturing towards ‘zero emission’ processes, with many alternatives under investigation. The European Commission has published the report ‘A Clean Planet For All’, described as a “strategic long-term vision for a prosperous, competitive, modern and climate neutral economy.” It talks about aims for a net zero emission of greenhouse gases by 2050, instead of the 80% CO2 reduction laid out in the climate change Paris Agreement (2016). Despite this, the 2030 emission targets have not been revised.
Considering that commodity glass melting furnaces for flat and container glass manufacturing have a lifetime of 15 to 20 years, 2030 is only one furnace lifetime away, 2050 perhaps only two. Many have proposed the use of electric boosting in all-electric melting furnaces as a possible immediate solution. This is because it is already more-or-less established technology, in use for smaller batches of speciality glass. However, there is currently no established technology that produces pull rate levels of 400-1000 tons/day, the production volume of traditional fossil fuel fired furnaces.
If the industry is to change to a different method of glass melting, new configurations can also be considered. Smaller container glass manufacturing furnaces with a pull rate of roughly 160 tons/day could be configured in a way such that a single, large IS machine is fed from a furnace in a one furnace, one forehearth, one IS machine set-up, instead of a traditional large furnace feeding multiple IS machines. Paralleling multiple smaller melting units could then also be a solution to applications requiring larger pull rates.
The recent GlassTrend Hydrogen Study Tour (reported by Anne-Jans Faber in Glass Worldwide May/June 2019 – see accompanying image showing the tour group) highlighted alternative ‘green’ heating methods and compared them against electrical boosting. Opinions are easily influenced when shown a specific direction and some participants consider hydrogen as a ‘holy grail’ in cleaner energy.
These opinions can perhaps be formed without looking into possible disadvantages and technological hurdles that come with using hydrogen as a solution. It should be kept in mind that there are no hydrogen combustion commodity glass melting tanks in operation right now, although that does not mean that it could not develop and be a good technology too!
It would be a great advantage if the industry could simply switch from natural gas or oil to hydrogen firing furnaces with no need to change the installed base. Unfortunately, that is not the case. To burn hydrogen in a furnace, new burner technology needs to be developed and it is very likely that the whole combustion process needs to be redesigned to accommodate the different properties of a hydrogen flame.
It would also be a mistake to assume that the reaction of hydrogen and air only leads to water emissions. Using hydrogen in a traditional, highly efficient, regenerative furnace would result in the hydrogen and preheated air also reacting to create nitrogen oxide (NOx) emissions, as shown in this equation:
H2 + O2 + N2 H2O + NOx.
Nitrogen oxides could be avoided by using pure oxygen in an oxy-fuel type furnace but this would result in lower efficiencies. In addition, oxygen would either need to be produced on-site, or the furnace facility would need to be close to an oxygen network. An alternative could be to carry out electrolysis on-site, using both the hydrogen and oxygen from this process for combustion. If this is a chosen method, the power grid must also be capable of bringing in the necessary energy to run an electrolyser, with large enough local hydrogen and oxygen storage facilities to maintain operations during a ‘Dunkelflaute’ (loss of energy from a lack of wind and solar sources). However, will such a complex system be economically feasible on a relatively small scale?
Although there is a debate for the use of electrons or atoms in the move to reduce CO2 emissions, importantly the technology needs to be both commercially viable and technologically feasible. With this in mind, renewable energy will predominantly come from wind or solar energy. In an all-electric solution, electrical grid constraints and the transmission losses of such a network should be considered. Fortunately, transmission losses are low. According to IndexMundi (2015), average electrical energy transportation and transformation energy losses in the Netherlands are shown to be approximately 4%, with 5.7% for Germany, and 6% for mid-Europe.
The glass industry already operates extremely efficient, all-electric furnaces that are capable of a low energy use of 2.7GJ/ton, compared to traditional furnaces that have an approximate consumption of 3.8 GJ/ton. Before jumping to the conclusion that an all-electric furnace is a perfect solution, however, the technology’s main disadvantage should be remembered, namely that electrical energy is difficult to store and that the continuous glassmaking process will not allow for long energy interruptions.
In contrast, hydrogen can be stored when cooled down to -253°C or compressed to 700 bars. Hydrogen does not exist in nature and needs to be generated. This electrolysis process has a maximum efficiency of 80%. Blue hydrogen could be made from natural gas but this process generates CO2 and should only be considered if carbon capture and storage techniques are feasible and available.
Hydrogen storage challenge
As mentioned earlier, it would be ideal to have hydrogen and oxygen produced from an electrolysis process on-site, mitigating nitrogen oxide formation in an oxy-fuel process. Still up for debate would be how to solve grid capacity and efficiency.
The centralised storage of hydrogen converted using surplus solar and wind energy could be an answer but this conversion process may not be the most efficient. Compressing or cooling hydrogen and oxygen for storage would also lead to a decrease in efficiency. Having both gases available during glass manufacture would require the plant to be near a storage point or would need a separate network of oxygen pipelines to be installed.
The question here is whether it would be more efficient to leave storage and gas transportation via pipelines to the utilities, which are capable of converting on a large-scale, while the glass industry focuses on all-electric solutions.
Need for greater objectivity
So what are the answers to this electron versus atom debate? The background of individual authors biases many of today’s articles about hydrogen. Glassmakers should digest and weigh up the options with that in mind, including this article.
Various studies exist on the subject and perhaps the main conclusion that comes to the surface is that more analysis is required from a range of parties to bring the topic to a level of more acceptable objectivity. The Energy and Sustainability Services team at Schneider Electric can shine a light on how the energy, hydrogen and CO2 markets are likely to develop in the future. It comes down to economics, because it makes no sense to design a plant that produces CO2-free glass but is prohibitively expensive and can draw no customers. Equally, it does not make sense to develop technologies for an energy source that is not readily available, or also too expensive.
The decision for atoms, electrons, or a combination of the two can only be based on economics, involving all parties in the supply chain; from raw materials to manufacturers, bottlers and end users.
To obtain a ‘clean planet for all’, complex problems need to be solved and the input of many disciplines is required to become successful. Without working together outside individual comfort zones and by thinking outside of the traditional glass manufacturing box, it is unlikely that success will be reached. The bottom line remains the same though. Despite these challenges, all parts of the glass industry need to work together to find a way for the industry to survive, to make sure that our children can still enjoy a cool beer out of a glass bottle with zero emissions.
This article appeared in the July/August 2019, issue 84 of Glass Worldwide.
About the Author:
René Meuleman is Business Leader for Global Glass
Lois Holman is the Product Marketing Intern for Eurotherm
Eurotherm Ltd, Worthing,
UK email: email@example.com